Polishing apparatus and method for producing semiconductors using the apparatus

ABSTRACT

The present invention relates to a polishing apparatus, and a semiconductor manufacturing method using the apparatus. Dressing of a grindstone surface is ground by sizing processing whereby dressing of a tool surface can be done while preventing occurrence of cracks on the grindstone surface which is the cause for occurrence of scratches. Further, flatness of the surface of a dressing tool can be guaranteed because of sizing cutting-in; even if a thick grindstone of a few centimeters is used, the flatness can be maintained to the end; and processing with less in-face unevenness can be always carried out. Therefore, the life of the dressing tool can be greatly extended.  
     Further, the present sizing-dressing is carried out jointly with processing of a wafer to thereby enable improvement of throughput of the apparatus as well as maintenance of a processing rate.  
     The present apparatus and method are effective for planarization of various substrate surfaces having irregularities.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This is a continuation of U.S. application Ser. No. 09/462,912,filed on Oct. 28, 1998, the disclosure of which, in its entirety, ishereby incorporated by reference.

FIELD OF THE INVENTION

[0002] The present invention relates to a planarization technique for awafer surface pattern by polishing processing used in the process ofmanufacturing a semiconductor integrated circuit, and particularly, to aprocessing method for the planarizing with high accuracy, highefficiency, and inexpensively without occurrence of processing damage,and a processing apparatus therefor.

BACKGROUND OF THE INVENTION

[0003] Recently, a multi-layer wiring technique for laminating circuitelements of a semiconductor device is becoming important with the trendof higher processing speed and fineness of a semiconductor device. Withthe progress of the multi-layer wiring technique, there has been posed aproblem of irregularities formed on the surface of a sample. Forexample, in the case where a circuit pattern is formed on the samplesurface by an optical exposure device (hereinafter referred to as astepper), it is necessary to accurately adjust the focal point of thestepper onto the sample surface. However, when the irregularities arepresent on the sample surface, adjustment of the focal point on thesample surface is difficult, resulting in an occurrence of seriousproblem of inferior resolution.

[0004] For overcoming such an inconvenience as described above, thetechnique for planarizing the surface of a semiconductor device has beendemanded.

[0005] In Japanese Patent Laid-open No. Hei 10-146750, there isdisclosed a technique for planarizing the fine irregularities formed onthe surface of a semiconductor device. According to the techniquedisclosed in the publication, a wafer substrate to be processed held ona rotating holder is pressed on the surface of a polishing pad held on arotating table, and a polishing liquid containing loose abrasive grainis supplied between the polishing pad and the wafer to be processed,whereby the surface of the semiconductor wafer substrate can be polishedto planarize the fine irregularities.

[0006] Since the polishing pad used for the purpose of polishing asdescribed above becomes crushed in surface as it is used, dressing iscarried out therefor with suitable frequency. Dressing termed herein isthat a polishing pad is shaved by a diamond grindstone (hereinafterreferred to as a dressing tool) or the like for dressing to provide asuitable surface roughness, as disclosed in Japanese Patent Laid-openNo. Hei 10-180618.

DISCLOSURE OF INVENTION

[0007] Dressing of a polishing tool as described above is carried out byapplying a fixed load to a grindstone to press it to the rotatingpolishing tool. However, the dressing carried out in the prior art asdescribed above is merely to realize formation of a surface roughness ofthe polishing tool.

[0008] On the other hand, if an attempt is made to prolong the servicelife of the polishing tool, it is necessary to thicken or harden thepolishing tool. However, there has occurred another problem as thehardness of the polishing tool increases, which has not occurred in theprior art.

[0009] The present invention has been achieved in order to solve theproblem as noted above.

[0010] According to the present invention, there is provided a polishingapparatus which applies relative motion between a workpiece and apolishing tool to polish the surface of the workpiece by the polishingsurface of the polishing tool, comprising: a dressing tool for forming asurface roughness on the polishing surface of the polishing tool; afirst moving means for applying relative motion between a grindstone andthe polishing tool; a second moving means for moving the dressing toolrelatively in a direction vertical to the polishing surface of thepolishing tool to locate it to a desired position; and a control meansfor permitting to execute the movement caused by the first moving meanswhile controlling the position of the second moving means.

[0011] The problem, action and effect of the present invention will bedescribed in detail in the column of made for carrying out the inventionthat will appear later.

BRIEF DESCRIPTION OF DRAWINGS

[0012]FIG. 1 is an explanatory view of the planarization step for thewafer surface.

[0013]FIG. 2 is a view of assistance in explaining a chemical mechanicalpolishing method.

[0014]FIG. 3 is a view showing a plane and a section of a semiconductormemory element.

[0015]FIG. 4 is a view of assistance in explaining a problem whenprocessing is accomplished using a soft polishing pad.

[0016]FIG. 5 is a view of assistance in explaining the constitution of agrindstone used in fixed abrasive grain processing method.

[0017]FIG. 6 is a view of assistance in explaining a conventionaldressing method in the fixed abrasive grain processing method.

[0018]FIG. 7 is a view of assistance of explaining the dressing methodaccording to the present invention.

[0019]FIG. 8 is a view showing the construction of a processingapparatus suitable for carrying out the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0020] The embodiments of the present invention will be describedhereinafter with reference to the drawings.

[0021] The semiconductor manufacturing step comprises many processingsteps. First, the wiring step which is one example of the steps to whichthe present invention is applied will be described with reference toFIG. 1.

[0022]FIG. 1A is a sectional view of a wafer formed with wiring of afirst layer. An insulating film 2 is formed on the surface of a wafersubstrate 1 formed with a transistor portion on which a wiring layer 3such as aluminum is provided. Since the insulating film 2 is providedwith a hole in order to take a junction with a transistor, that portion3′ of the wiring layer is somewhat depressed.

[0023] In the wiring step of a second layer shown in FIG. 1B, aninsulating film 4 and a metallic aluminum layer 5 are formed on thefirst layer, and a photoresist layer 6 for exposure is adhered theretofor wiring-patterning the aluminum layer.

[0024] Next, as shown in FIG. 1C, a circuit pattern is transferred inexposure on the photoresist 6 using a stepper 7. In this case, when thesurface of the photoresist layer 6 has irreguralities, focusing is notobtained on a concave portion and a convex portion 8 on the photoresistsurface simultaneously as shown, resulting in an importance obstacle orinferior resolution.

[0025] For overcoming such an inconvenience as described, planarizationprocessing for the substrate surface is carried out as mentioned below.After the processing step shown in FIG. 1A, an insulating layer 4 isformed, as shown in FIG. 1D, after which polishing processing is carriedout by a method described later so as to be planar to a level 9 shown toobtain a state shown in FIG. 1E. Thereafter, a metallic aluminum layer 5and a photoresist layer 6 are formed, and exposed by a stepper as shownin FIG. 1F. Since in this state, the photoresist surface is flat, noproblem in the inferior resolution occurs.

[0026] In the following, an outline of the fixed abrasive grainprocessing apparatus suitable for employment of polishing processingaccording to the present invention will be explained while comparingwith the chemical mechanical processing apparatus that has generallybeen used heretofore.

[0027] (1) Outline of Chemical Mechanical Polishing Apparatus

[0028] The surface planarizing apparatus for the semiconductor devicesurface as disclosed in Japanese Patent Laid-open No. Hei 10-180618 iscalled a chemical mechanical polishing (Chemical Mechanical Polishing:CMP) apparatus. As described above, in this apparatus, a polishing padheld on a rotating member is pressed against a semiconductor device heldon a rotating sample table, and a liquid containing a polishing slurryis allowed to flow between the polishing pad and a sample to therebypolish and planarize the surface of the semiconductor device.

[0029]FIG. 2 is a view showing the principle of polishing asemiconductor device by a CMP apparatus. First, a polishing pad 11 isattached onto a surface plate 12 and remains rotated. This polishing padis formed by slicing foamed urethane resin or the like into a thinsheet, and materials and fine surface construction thereof are variouslyselected and used according to kinds of workpieces and a degree ofsurface roughness suited to finishing.

[0030] A wafer to be processed (a semiconductor device) 1 is fixed to awafer holder 14 through an elastic keeping pad 13. The wafer holder 14being rotated is loaded on the surface of the polishing pad 11, andpolishing slurry 15 is supplied onto the polishing pad 11 to therebypolish and remove a convex portion of an insulating film 4 on the wafersurface to planarize it.

[0031] As described above, the CMP is a method for carrying outprocessing while supplying the polishing slurry between the polishingpad and the workpiece, which method is extensively known as looseabrasive grain polishing technique but has three great problems notedbelow.

[0032] A first problem is dependence on pattern dimension, that is, itmay be impossible to be sufficiently planarized depending on kinds ofpatterns or a state of level difference. Generally, a pattern on thesemiconductor wafer is formed from a pattern having various dimensionsand level difference.

[0033] For example, as for an example of a semiconductor memory element,a chip is divided into four blocks, as shown in FIG. 3A. The four blocksare internally formed with fine memory cells which are regularly andclosely arranged, which is called a memory mat portion 16.

[0034] In a boundary between the four memory mat portions is formed aperipheral circuit 17 for getting access to the memory cells. In case ofa typical dynamic memory, a dimension of one chip is approximately 7mm×20 mm, and width of the peripheral circuit portion is approximately 1mm. In section A-A′ of the chip, average height of the memory matportion 16 is higher by approximately 0.5 to 1 μm than that of theperipheral circuit portion 17, as shown in FIG. 3B. When an insulatingfilm 4 having thickness of approximately 1 to 2 μm is formed on suchlevel difference pattern, a sectional shape 31 of the surface portionalso substantially reflects a level difference shape of the basepattern.

[0035] In the planarization step for a semiconductor wafer, theinsulating film 4 on the wafer surface is to be planarized as indicatedby dotted lines 32. However, generally, where a soft polishing pad 11Lmade of foamed urethane resin which is often used for the aforesaid useis used, planarizing as described above cannot be achieved as thepolishing speed depends on a pattern. That is, where the soft polishingpad 11L is used as shown in FIG. 4, a surface shape of the polishing padis deformed as indicated by the solid line in the figure due to thepolishing load. In a fine pattern whose dimension is in micrometersorder, a load is concentrated thereon, and planarization polishing isdone in a short period of time, whereas in a fine pattern whosedimension is in a few milimeters order, a load is applied as adistributed load so that polishing speed is low. As a result, asectional shape after polishing is as indicated by wave lines 34 in FIG.4 so that height difference d still remains.

[0036] For use of the wiring step of a semiconductor, unevenness±5% orless is desired, and an upper limit of hardness of the polishing pad isapproximately Young's modulus: 10 kg/mm².

[0037] Therefore, in semiconductor elements in which various patternsfrom a few milimeters order to micrometers order are mixed as in amemory element, sufficient planarization effect cannot be expected.Applicable objects are limited to semiconductor products including apattern not being excessively large size, for example, such as a logicLSI.

[0038] A second problem in the planarization technique of a looseabrasive grain system is that running cost is high. This results fromlow utilization efficiency of the polishing slurry in the loose abrasivegrain polishing method. That is, it is necessary for super-smoothpolishing free from occurrence of polishing scratch to supply polishingslurry such as colloidal silica in a rate of hundreds cc/min or more,most of which are however removed without contribution to actualprocessing.

[0039] The price of high-purity slurry for a semiconductor is very high,and most of cost for the planarization polishing process is determinedby quantity of using the polishing slurry, improvement of which istherefore strongly demanded.

[0040] A third problem is that the life of a polishing pad is short,which results from dressing work for the surface of the polishing pad.At present, it is necessary to replace a polishing pad every 500 wafers.

[0041] (2) Outline of Fixed Abrasive Grain Polishing Apparatus

[0042] For solving the problem with respect to the loose abrasive grainpolishing as described above, there is a polishing method by means ofthe fixed abrasive grain polishing employed in an apparatus of anembodiment of the present invention.

[0043] The fixed abrasive grain polishing technique employed in theapparatus of the embodiment of the present invention uses, in thepolishing apparatus shown in FIG. 2, a special grindstone 20 whosehardness is controlled optimally in place of the conventional polishingpad.

[0044] More specifically, elastic modulus of the grindstone 20 is 5 to500 kg/mm², and the hardness thereof is {fraction (1/10)} to {fraction(1/100)} of that of a conventional grindstone that has been used inother fields. On the other hand, the hardness of the grindstone 20 is 5to 50 times that of a hard polishing pad such as hard foamedpolyurethane that has been used for the present invention.

[0045]FIG. 5 shows the construction of a grindstone used in theaforementioned technique. Abrasive grain 21 is preferably formed ofsilicon dioxide, cerium oxide, aluminum oxide, etc., and if grain sizethereof is approximately 0.01 to 1 μm, excellent processing efficiencycan be obtained without occurrence of scratches.

[0046] It is said to be preferable that resin 22 for joining theabrasive grain is high purity organic resins of a phenol family, apolyester family or the like. The abrasive grain is mixed into thejoining resin, after which proper pressure is applied thereto tosolidify it, and processing such as heating and hardening is applied asnecessary. In the aforesaid process, hardness of the grindstoneresulting from the kind of the joining resin and the magnitude ofpressurization can be controlled, and in the present art, this is to be5 to 500 kg/mm².

[0047] In the case where pure water as polishing liquid is supplied to agrindstone fabricated by joining the cerium oxide abrasive grain having1 μm of grain size with the phenol family or polyester family resin sothat elastic modulus is 100 kg/mm², which is used to process a silicondioxide film having a 1 μm of thickness. In this case, no scratchoccurs, and there can be obtained extremely excellent planarizationperformance, which processing speed is 0.3±0.011 gm or less with respectto all kinds of patterns whose pattern width is from 10 mm to 0.5 μm.

[0048] Coexistence of the scratch-free processing and the excellentplanarization performance can be achieved first by the fixed abrasivegrain processing using the grindstone whose elastic modulus isoptimized.

[0049] Further, in the loose abrasive grain processing, the polishingpad has a life of approximately 500 wafers. However, in theabove-described art, the thickness of the grindstone can be a fewcentimeters, and therefore, the life of the grindstone can be extended,which ends to approximately 15000 wafers.

[0050] This means that the frequency of replacing a polishing pad can bereduced to “from every day to every month”, i.e., {fraction (1/30)},which is an extremely great merit in a site in which products are madein a large volumes.

[0051] The planarization method using the aforementioned grindstone as apolishing tool has many merits, but it has been found that new problemsoccur because of the fixed abrasive grain processing.

[0052] A first problem is a problem of maintaining processing efficiencyof the grindstone surface. Also in the planarization technique using theabove grindstone, similar to the planarization polishing by way of looseabrasive grain, blinding occurs in the grindstone surface as wafers arepolished, and dressing for the grindstone surface is sometimesnecessary. For this dressing, scratching processing by way of constantpressure load has been used heretofore.

[0053] Specifically, as shown in FIG. 6, a conditioning ring 42 withdiamond grain 41 from #80 to #400 embedded is slidably moved at relativespeed from 5 to 30 cm/s on the surface of a grindstone 20 while loadingunder average surface pressure from about 100 to 300 g/cm². Thereby, theedge of the diamond grain 41 uniformly scratches the grindstone surface,thus enabling carrying out dressing for the grindstone surface.

[0054] However, it has been found that when the surface of a grindstoneis subjected to dressing, similar to the polishing pad of the CMP, sharpcracks 43 having depth of a few tens of micrometers occur on thegrindstone surface, and the crack end triggers breakage of thegrindstone end during the polishing processing, finally leading tooccurrence of large cracks in micrometers order. It is supposed that theoccurrence of cracks results from the fact that the size of the diamondgrain 41 is large, such as #80 to #400, that is, grain size: 300 μm to60 μm. Further, this abuse also results from the fact that the hardnessof the wafer polishing grindstone 20 is high.

[0055] So, if the diamond grain size is made smaller, this problem canbe solved. However, there occurs a further serious problem in this case.That is, it becomes difficult to adhere the diamond grain 41 to the basering 42 so that the diamond grain is disengaged during the dressingoperation and embedded into the grindstone surface, resulting inoccurrence of scratches.

[0056] The phenomenon of occurrence of cracks on the surface of apolishing tool is a unique phenomenon occurring only at the time ofdressing of a grindstone whose mechanical property is adjusted to beused for planarization of a semiconductor, and such a phenomenon asdescribed has not occurred at the time of dressing a polishing padformed of a polyurethane resin or the like which is a ductile material.

[0057] A second problem is deterioration of a planarization degree ofthe grindstone surface. A conventional general dressing method is basedon the processing principle of scratching diamond grain while pressingthem into the grindstone surface under a constant load, and has itsobject to apply a constant load to a conditioning ring irrespective ofchange in height or inclined attitude of the grindstone surface tocreate a uniform surface roughness.

[0058] To this end, generally, it is constructed that as shown in FIG.6, a constant pressure load by way of an air cylinder or the like isapplied to a conditioning ring 42 through a gimbals support 44.Therefore, where hardness distribution of the grindstone is uneven orthe number of revolutions of the conditioning ring is deviated from aset value, dressing amount distribution in a radial direction of thegrindstone is uneven so that about the time when the grindstone havingapproximately 20 mm of initial thickness is dressed to approximately 10mm of thickness, a shape of the grindstone surface is formed into ashallow cone-shape or an inverted Mt. Fuji shape in tens of micrometersorder. When the flatness of the grindstone surface is deteriorated asdescribed, processing unevenness occurs in the wafer surface to beprocessed, resulting in an important defect.

[0059] If an attempt is made to obtain processing evenness of 5% withthe planarization by way of fixed abrasive grain processing, it isnecessary that the flatness of the grindstone is in a few micrometersorder.

[0060] The above-described problem of the flatness of the grindstoneoccurs also when a new grindstone is used. That is, it is very difficultfor a large grindstone having a diameter of 70 cm or more and athickness of a few centimeters to fabricate in a few micrometers orderof the flatness of the surface to be polished and to mount on thepolishing apparatus, and the inferior flatness at that time wasimpossible to be corrected by a conventional constant pressure dressingmethod. Further, in the case where the grindstone is divided into aplurality of segments for the convenience of manufacture and mounting ofthe large grindstone, level difference, between the segments, in tens ofmicrometers order cannot be avoided, which also leads to a seriousproblem.

[0061] A problem in the flatness of the surface of the polishing tool asdescribed above is a problem peculiar to the case where a grindstonehaving a thickness of a few centimeters is used, which could be almostignored in a general polishing pad for loose abrasive grain processingin which elastic modulus of a pad material is soft such as 10 kg/mm² orless and thickness is thin such as approximately 1 mm.

[0062] Further, even where the flatness may pose a problem somewhat, itcould be sufficiently dealt with by a simple correcting control suchthat the time for dressing convex portions on the surface of a polishingpad is slightly prolonged or loads are increased.

[0063] As explained so far, in the wafer planarization step by way offixed abrasive grain processing, there poses many problems in theconstant pressure dressing method used in the planarization step by wayof a conventional general loose abrasive grain processing, and thesolution for such problems is strongly desired.

[0064] (3) Outline of Apparatus According to Embodiment of the PresentInvention

[0065] The apparatus according to an embodiment of the present inventionis to solve the problem peculiar to the apparatus for polishing thesurface of a semiconductor device by a hard polishing tool such as usedfor the aforementioned fixed abrasive grain processing. This will beexplained hereinafter with reference to the drawings.

[0066]FIG. 7 shows a concrete example for carrying out the presentinvention. In the drawing, a wafer holder for a wafer (a workpiece)which is an object to be polished is omitted.

[0067] A small diameter (50 mm) cup-shaped diamond grindstone 101 (adressing tool) having diamond grain 41 of #100 fixedly mounted on theedge thereof is driven by a spindle motor 102 and rotates at high speedof 10000 rpm to apply dressing to a polishing surface of a waferpolishing grindstone 20 (a polishing tool) which rotates at speed ofapproximately 10 rpm. By the aforesaid high speed rotation, theperipheral speed of the diamond grindstone 101 reaches approximately 20m/s to enable dressing of the grindstone surface with sufficiently smallroughness.

[0068] In this case, the cut-in amount of the diamond grindstone 101 isin micrometers order, typically, 1 μm.

[0069] The spindle motor 102 is provided on the Z moving table 103, andis driven by a Z driving system 104 (a second moving means) to move in aZ axis direction to enable positioning at a suitable position. Since theZ moving table 103 is controlled in movement in an X axis direction onan X moving table 105 to be moved in the X axis direction by means of anX moving system 106, the diamond grindstone 101 is moved straight in aradial direction of the grindstone while maintaining the cut-in amount(a position in the Z axis direction of the diamond grindstone) by themovement of the X moving table.

[0070] A rotating means for rotating the spindle motor 102, the X movingtable 105 or the wafer polishing grindstone is to impart relative motionbetween the diamond grindstone 101 and the grindstone 20, andcorresponds to a first moving means of the present invention. It isnecessary that an error in motion of the shaft perpendicular to themoving shafts of these moving means is sufficiently small as comparedwith the cut-in amount.

[0071] The upper surface of the grindstone 20 is ground into an accurateplane by grinding the sample surface (hereinafter referred to assizing-dressing) while maintaining the position of the Z axis directionof the diamond grindstone 101. In this case, the cut-in amount of thediamond grindstone 101 is determined by a positioning coordinate of theZ moving table 103 and is given by instructions of the control system107.

[0072] While in the apparatus according to the embodiment of the presentinvention, a moving system for moving the diamond grindstone 101 in theZ direction, it is noted that the wafer polishing grindstone 20 may bemoved in the Z direction so that a fixed cut-in amount will bemaintained. Also, with respect to the movement in the X direction, thewafer polishing grindstone 20 may be moved.

[0073] The diamond grain 41 arranged and secured to the processingsurface of the diamond grindstone 101 assumes a state of sticking intothe wafer polishing grindstone 20 when the cut-in amount is set by the Zmoving system 104. When in that state, the diamond grindstone 101rotates, the diamond grain 41 grinds the surface of the wafer polishinggrindstone 20 while maintaining the position of the Z direction thereof.

[0074] The surface processing for the wafer polishing grindstoneconstructed as described above is carried out in the following manner.First, prior to the wafer polishing, when an instruction for startingthe dressing work is given, the polishing grindstone 20 starts torotate. At the same time, the control device 107 gives the Z drivingsystem an instruction of movement in the cut-in direction till thediamond grindstone 101 comes in contact with the grindstone surface.Note that elements (not shown) for detecting the aforesaid contact statemay be any means, such as a contact type sensor, or a noncontact sensorsuch as an optical type, and the spindle motor 102 is preferablyrotating.

[0075] When the contact therebetween is assured, the control device 107gives an instruction of 1 μm of cut-in, and at the same time, gives theX-axis driving system 106 a continuous movement instruction at speed ofapproximately 10 mm/s. The X moving table 105 reciprocates by thedistance one half diameter of the grindstone 20, and the diamondgrindstone 101 grinds and removes the whole grindstone surface by 1 μm.Thereby, the grindstone surface is subjected to dressing. The times ofreciprocation, moving speed and cut-in amount of the X moving table, andthe rotational speed of the grindstone 20 are set to the optimalconditions while adjusting to the kind of grindstones. Preferably, purewater as processing liquid for grinding is supplied during the dressingwork. Further, waste liquid and sludge remaining on the grindstonesurface are preferably removed by vacuum attraction.

[0076] Preferably, setting of the times of reciprocation is decided onthe basis of cut-in allowable depth capable of sticking the diamondgrain 41 into the wafer polishing grindstone 20 (limit depth in whicheven if the extreme ends of the diamond grain 41 is stuck into thesurface of the wafer polishing grindstone 20, the grindstone is notbroken microscopically). For example, where the cut-in allowable depthis 0.5 μm, when the grindstone surface is desired to be removed by 1 μmby dressing, at least twice (one reciprocation) movements of the Xmoving table 105 is necessary.

[0077] As described above, where a large cut-in amount is desired to beobtained, it is suggested that stepwise control of position by the Zdriving system 104 be carried out. For example, where cutting-in of 2μm, cutting-in of 0.5 μm may be repeated four times for dressing. Suchdressing work may be carried out in advance prior to processing of aworkpiece, or may be carried out during processing together withprocessing. Particularly where dressing is carried out stepwise asdescribed above, if dressing is carried out together with processing,throughput of apparatus is not impaired.

[0078] While in the foregoing, a description has been made of the casewhere in a state that a positioning coordinate of the Z moving table 103be fixed, a dressing tool is X-moved to plane-process the surface of thepolishing grindstone 20, it is to be noted that the positioningcoordinate of the Z moving table 103 is numerical-controlledcorresponding to the X coordinate of the X movement whereby the surfaceof the polishing grindstone 20 can be formed into a curve surface otherthan a plane.

[0079] In carrying out the present invention, to select the diamondgrain 41 of the dressing tool is very important, and an excessivelysmall or excessively large diamond grain 41 is not preferable. That is,while a dressing tool including lots of diamond grain having a smallgrain size is efficient because of many cutting edges, the diamond grainis liable to be disengaged due to cutting force, possibly resulting inthe fatal cause of scratches. Conversely, in a dressing tool with lessdiamond grain having a large grain size, there is no possibledisengagement of diamond grain. However, since the number of cuttingedges is small, efficiency lowers unless the number of revolutions ofthe tool is increased.

[0080] While in the foregoing, the extreme ends of the diamond grain issharp as in a point, it is to be noted that if the extreme ends are inthe form of a flat edge, high efficiency can be obtained even if thenumber of diamond grain is small. Tool edges having a flat edge-likeextreme end as described include a diamond cutting tool or a carbidecutting tool used in mirror-face grinding. Even a dressing tool of thetype which rotates a detachable and small cutting tool as described at ahigh speed may provide good result.

[0081] According to the sizing-dressing of the apparatus of the presentinvention, dressing of the grindstone surface and planarization of thegrindstone surface can be realized simultaneously, and adequate settingof the cut-in amount enables realization of dressing of a high hardnessgrindstone and planarization without occurrence of cracks in a waferpolishing grindstone.

[0082] The occurrence of cracks in the wafer polishing grindstone 20 inthe present apparatus can be suppressed because the diamond grindstone101 formed on the processing surface of the present apparatus with thediamond grain 41 performs polishing so as to scrape the circumference(the surface of the wafer polishing grindstone 20) in a state ofmaintaining the cut-in amount (depth) constant. That is, because, byadequate setting of the cut-in amount, the scratch-crushing force withrespect to the wafer polishing grindstone 20 can be suppressed to alevel below a fixed value against a microscopic construction change inthe grindstone caused by the presence of pores or the like.

[0083] On the other hand, in the case of application of a polishingmethod by constant pressure load used so far, the diamond grindstone ispressed under constant pressure against the wafer polishing grindstone,generally. However, microscopically, discontinuous cut-in depth resultsdue to the presence of pores or the like so that cracks sometimes occurby exceeding the allowable cut-in depth instantaneously.

[0084] As described in detail above, in the present apparatus of thepresent invention, even in the case where a high hardness grindstone asused in the fixed abrasive grain processing is employed, the problem asnoted above can be overcome by fixing the wafer polishing grindstone andthe relative position in the Z direction of the polishing tool.

[0085] Further, according to the sizing-dressing of the presentinvention, the planarization of the surface of the wafer polishinggrindstone can be realized with higher accuracy as compared with theconventional polishing by the constant pressure load.

[0086] The polishing by the constant pressure load has a problem in thatrelatively fine undulation on the surface of the wafer polishinggrindstone can be removed, but smooth undulation on the surface of thewafer polishing grindstone cannot be removed. This is because thediamond grindstone is moved so as to trace the smooth undulation of thewafer polishing grindstone merely by applying pressure. Particularly, inthe apparatus in which the wafer polishing grindstone 20 is considerablylarger in size than the diamond grindstone 101 shown in FIG. 7, it iscontemplated for example that a convex portion (or a concave portion)wide in the hem occurs from end to end of the wafer polishing grindstone20, which abuse sometimes becomes more notable.

[0087] On the other hand, in case of the sizing-dressing according tothe present invention, the surface of the wafer polishing grindstone canbe ground without being influenced by the irregularities of the surfaceof the wafer polishing grindstone, thus enabling planarization with highprecision of the wafer polishing grindstone.

[0088] In applying the sizing-dressing, attention should be paid to thefact that excessive pressure is not applied to the wafer polishinggrindstone. That is, attention should be paid to the fact that the waferpolishing grindstone is not pressed against the diamond grindstone underexcessive pressure by setting the cut-in amount having excessive depth.

[0089] The control of the Z driving system by the element for detectingthe contact state between the diamond grindstone and the wafer polishinggrindstone, as described above, is carried out so that excessivepressure is not applied to the wafer polishing grindstone.Alternatively, a means (not shown) for detecting pressing force of thediamond grindstone may be provided in advance whereby when pressingforce in excess of a fixed level is detected, the diamond grindstone isonce moved away from the wafer polishing grindstone to generate an erroror re-set a proper cut-in amount for carrying out polishing again.

[0090] There is another operating method which performs dressingsimultaneously with planarization polishing of wafer. The operatingmethod includes one mode in which the above operation carries out onceduring processing one wafer, and the other mode which always carries outdressing while increasing the cut-in amount continuously also duringprocessing. For those requiring low-speed dressing according to the kindof grindstones, the latter mode is preferable.

[0091] It has been found after dressing of a grindstone whose abrasivegrain is cerium oxide under the conditions of the aforementionedembodiment that cracks that occurred at a level of three per 10 cm inthe conventional method disappeared, and no scratch occurred.

[0092] Further, with respect to maintenance of the flatness of theprocessing surface of a grindstone, it is possible to obtain theflatness of 5 μm over the whole grindstone surface, which value has notbeen lowered even by about 5000 times of dressings, that is, by dressingtill thickness of a grindstone reduces by 10 mm.

[0093] Further, it is contemplated that polishing by constant pressureload that has been used in the past and sizing-dressing are jointly usedwithin a single apparatus.

[0094] In this case, it is suggested that the polishing by a constantpressure load or the sizing-dressing can be selected depending on use ofthe wafer polishing grindstone or the polishing pad that has been usedin the conventional CMP apparatus.

[0095] For example, in the apparatus shown in FIG. 7, it is suggestedthat the apparatus be set so that when a wafer polishing grindstone (ora polishing pad) is replaced, an operator inputs use of the waferpolishing grindstone or the polishing pad through an input unit notshown in FIG. 7 whereby whether the polishing by the constant pressureload or the sizing-dressing can be automatically selected.

[0096] Further, even a polishing pad that has been used in theconventional CMP, the sizing-dressing is sometimes suited depending onthe hardness thereof. Therefore, it is contemplated that the apparatusis set so that whether the polishing by the constant pressure load orthe sizing-dressing is automatically selected by inputting the kind ofpolishing tools.

[0097] By the constitution of the apparatus as described above, anoperator is able to easily set the adequate polishing conditions withoutknowing the principle of polishing by the constant pressure load or thesizing-dressing.

[0098] Next, an example of a concrete constitution of a processingapparatus suitable for carrying out the present invention will beexplained with reference to FIG. 8. Basically, this is a polishingapparatus comprising two platens and two heads, characterized in that agrindstone is used as a polishing tool, and that the art of the presentinvention for optimally dressing the grindstone is applied.

[0099] A grindstone which is high in planarization performance and isoptimized in elastic modulus is adhered to the upper surface of a firstgrindstone surface plate 51, and a finishing grindstone which is low inelastic modulus is adhered to the upper surface of a second grindstonesurface plate 52. These grindstone surface plates respectively polish awafer while rotating at fixed speed of about 20 rpm.

[0100] Prior to processing, dressing of the first grindstone surfaceplate 51 is carried out. A spindle motor 102 mounted on the extreme endof an oscillating arm 108 causes a small-diameter diamond grindstone 101to rotate at high speed of 10000 rpm, to dress the surface of thegrindstone surface plate 51 which is rotating at 20 rpm. Setting of acut-in amount is done by a Z moving device 103 at the base of theoscillating arm, typically, being cut in every 1 μm. An oscillatingperiod of the arm is about 30 seconds, and when this is finished, waferpolishing is ready.

[0101] While in the above embodiment, the arm oscillating type isemployed, it is apparent that the direct-operated type as shown in FIG.7 may be employed. Further, while in the above embodiment, an example isdescribed in which dressing is carried out prior to processing ofplanarization polishing. It is noted that this can be carried out duringprocessing as previously mentioned.

[0102] When dressing is finished, the step enters polishing of a wafer.A wafer 55 to be processed is taken out of a loader cassette 53 by ahandling robot 54 and is put on a load ring 57 on a direct-operatedcarrier 56. When the direct-operated carrier 56 moves leftward in thefigure and is positioned at a load/unload position, a polishing arm A58rotatively moves. The wafer 55 to be processed is then vacuum-adsorbedon the lower surface of a wafer polishing holder 59 provided on theextreme end thereof. Then, the polishing arm A58 rotates so that thewafer polishing holder 59 may position on the first grindstone surfaceplate 51. The wafer polishing holder 59 presses the wafer 55 to beprocessed being adsorbed on the lower surface against the grindstone toprocess it while rotating. When the first processing step is finished,the polishing arm A58 then rotates so that the wafer polishing holder 59may position on the second grindstone surface plate 52. Thereafter, thewafer polishing holder 59 rotates while pressing the wafer 55 to beprocessed being adsorbed on the lower surface against the secondgrindstone surface plate 52 to finish it.

[0103] Upon termination of the aforementioned two stages, the stepenters next cleaning step. The polishing arm A58 rotates to position thewafer polishing holder 59 on a cleaning position on which a rotationalbrush 60 is provided.

[0104] The rotational brush 60 washes the processing surface of thewafer 55 to be processed being adsorbed on the lower surface of thewafer polishing holder 59 by a washing brush while rotating. Uponcompletion of cleaning, the direct-operated carrier 56 again moves tothe cleaning position to receive the wafer to be processed released fromthe vacuum adsorption of the wafer polishing holder 59. While here, therotational brush is used, it is to be noted that a cleaning method byway of a jet water flow with supersonic waves can be used instead.Thereafter, when the direct-operated carrier 56 returns to theload/unload position, the wafer handling robot 54 grips a processedwafer, which is housed in an unload cassette 61.

[0105] One period of operation for the polishing arm A58 has beendescribed above. A polishing arm B62 is also jointly operated similarlyto the former. Naturally, this is because two polishing surface platesare time-divided for effective utilization. The operating sequence ofthe polishing arm B62 is exactly the same as that of the polishing armA58, but a phase is delayed only by one half period. That is, thepolishing arm B62 starts its operation while adjusting to the start ofthe second polishing step.

[0106] The above-described embodiment is an example of constitutionsuitable for the case where the number of polishing arms is two, and thedressing apparatus is only one system. This is the constitution in whichthere is provided a position where rotating traces of two polishing armscross or are in contact, and there is provided a stop position for apair of cleaning brushes and the direct-operated carrier for theload/unload, whereby these functions are jointly used by the twopolishing arms.

[0107] While in the above-described embodiment, only the first polishingsurface plate is proved for dressing, a rotating center position of thedressing apparatus can be changed as necessary so that the secondpolishing surface plate can be dressed, or a second dressing apparatuscan be separately provided.

[0108] While a description has been made of the embodiment in which twopolishing arms are provided, it is to be noted that naturally, a singlearm will suffice for simplifying the constitution. Conversely, forimproving the throughput of the apparatus, the number of polishing armscan be made three or more, or a plurality of wafer polishing holders canbe mounted on a single polishing arm.

[0109] Further, while in the above-described embodiment, two rotatingsurface plates are respectively independently provided for the polishingpad and for the grindstone, it is to be noted that a single rotatingsurface plate will also suffice. That is, a ring-like grindstone isprovided in the peripheral portion of the rotating surface plate, and afinishing grindstone is provided in the central portion thereof.

[0110] Further, a polishing grindstone or a polishing pad mounted on thepolishing surface plate is not always limited to an integral disk-likeform, but a combination of a plurality of segments may be used.Alternatively, it can be designed so that a rotating surface plate isinclined in order to make a foot pint (a projection area forinstallation) of apparatus small.

[0111] Further, the apparatus of the present invention can be applied tothe manufacture of optical elements having a fine surface constructionsuch as a semiconductor element, a liquid crystal display element, amicro machine, a magnetic disk substrate, an optical disk substrate, aFresnel lens and so on.

[0112] In the case where a semiconductor wafer is planarized by thefixed abrasive grain processing method using a grindstone as a polishingtool, dressing of the grindstone surface is carried out bysizing-dressing method of cutting-in in micrometers order, andtherefore, occurrence of cracks on the grindstone surface which is thecause of occurrence of scratches can be prevented.

[0113] Further, in this case, flatness of the grindstone surface isalways guaranteed because of the sizing cut-in, and polishing processingwithout occurrence of unevenness can be always carried out. As a result,further, thickness of a grindstone can be a few centimeters or more,enabling to greatly extend the life of grindstone.

[0114] Further, by continuously carrying out application ofsizing-dressing to a grindstone of the present invention also duringwafer processing, clogging during processing can be prevented, and theoverhead time necessary for dressing can be eliminated, thus enablingimprovement of throughput of apparatus.

[0115] While in the above description of the embodiment of the presentinvention, an example using a grindstone by way of the fixed abrasivegrain polishing method has been described, it can be readily imaginedthat even if that is applied to a polishing pad used in the conventionalCMP apparatus, substantially similar effect can be obtained. In thiscase, the effect of the present invention can be enjoyed to the maximumby using a (hard) polishing pad which is thicker and is larger inelastic modulus as compared with a prior art.

[0116] Furthermore, since in the apparatus of the present invention,planarization of a polishing tool and dressing can be carried outsimultaneously, it is possible to improve the throughput of apparatus.

[0117] Moreover, while in the foregoing, an embodiment in connectionwith a semiconductor wafer has been described, this can be also appliedto planarization processing of others such as a thin film video device,substrates formed of glass or ceramics, etc.

[0118] Further, in the present invention, the throughput of apparatus aswell as maintenance of processing rate can be improved by jointlycarrying out the wafer processing and the sizing-dressing.

[0119] According to the present invention, also in the fixed abrasivegrain processing method using a grindstone, occurrence of cracks can beprevented to dress the grindstone surface, and planarization processingwithout occurrence of scratches can be carried out. Further, theflatness of the grindstone surface can be guaranteed because of thesizing cut-in, and processing without in-face unevenness can be alwayscarried out. Therefore, a thick grindstone of a few centimeters can beused, enabling greatly extending of the life of a grindstone.

[0120] Furthermore, in the present invention, the presentsizing-dressing is carried out jointly with the wafer processing tothereby improve the throughput of apparatus as well as maintenance ofprocessing rate.

What is claimed is:
 1. A method for manufacturing a semiconductor foreffecting polishing-processing while pressing the thin film surfaceadhered to the surface of a semiconductor substrate formed with anirregularity pattern to the polishing surface of a polishing tool forrelative motion, comprising the steps of: forming a surface roughnesswith a dressing tool on the polishing surface of said polishing tool,during a period between said polishing-processing or during thepolishing-processor while controlling movement of said dressing tool ina vertical direction with respect to said polishing surface.
 2. A methodfor manufacturing a semiconductor according to claim 1, wherein saidforming step is performed each semiconductor substrate.
 3. A method formanufacturing a semiconductor according to claim 1, wherein saidmovement of said dressing tool in a vertical direction is limited insubstantially 1 μm.
 4. A method for manufacturing a semiconductoraccording to claim 1, wherein said movement of said dressing tool in avertical direction is limited between 0.5 and 2 μm.
 5. A method formanufacturing a semiconductor for effecting polishing-processing whilepressing the thin film surface adhered to the surface of a semiconductorsubstrate formed with an irregularity pattern to the polishing surfaceof a polishing tool for relative motion comprising a step of: forming asurface roughness with a dressing tool on the polishing surface of aidpolishing tool before said polishing-processing while controllingmovement of said dressing tool in a vertical direction with respect tosaid polishing surface.
 6. A method for manufacturing a semiconductorfor effecting polishing-processing while pressing the thin film surfaceadhered to the surface of a semiconductor substrate formed with anirregularity pattern to the polishing surface of a polishing tool forrelative motion comprising a step of: forming a surface roughness with adressing tool on the polishing surface of said polishing toolsimultaneously said polishing-processing while controlling movement ofsaid dressing tool in a vertical direction with respect to saidpolishing surface.